鱗の第１輪径からみた若狭湾西部海域におけるマダイ群の移出入

Abstract

The present paper deals with the changes in the radius composition of the first ring on the scale with age of red sea bream Pagrus major, and estimates its migration, or immigration and emigration patterns in Western Wakasa Bay, using fish 1 to 5 years of age in the 1991 year group and fish l to 4 years of age in the 1992 year group.Scale radius (Rin mm) was related to fork length (FL in mm) in each year group as expressed by the following equations, 1991 year group: ln FL=1.047ln R+3.4641992 year group: ln FL=1.041ln R+3.473In the compositions of the first ring radii on the scales in younger age-group (fish less than 3 or 4 years), it was revealed that the percentage occurrences of those with the small first ring radius (northern stock) increased with their ages, while the large first ring radius (southern stock) decreased. Based on the regional differences in the size of the first ring radius on the scale of l year-old fish, it is suggested that the northern stock migrates into Western Wakasa Bay and possibly mixes with local stock (the medium first ring radius) in the Bay. Based on the change in the estimated catch in numbers by age and three types of radius (large, medium and small radius) in the 1991 year group, at least about 30% to 70% of red sea bream at 4 years of age might participate in their immigration or emigration in Western Wakasa Bay.